An ink jet recording method is a recording method in which fine droplets of an ink composition are ejected so as to be applied to a recording surface of a recording medium such that printing is performed. This method has an advantage that a high-quality image can be speedily printed at high resolution. A printing technique using the ink jet recording method is employed in general consumer printers used in offices or the like and also employed in industrial printers having a print span of greater than 1 m. Examples of the recording medium include general paper sheets and hydrophobic recording media such as plastic films.
The reason why the ink jet recording method is employed in such industrial printers is that prints can be obtained at low cost even if the number of the prints is small, in addition to the above advantage of the ink jet recording method. In recent years, the ink jet recording method has been widely used to prepare indoor or outdoor trade signs, banners, wall coverings, and room decorations. Recording media and prints used for the indoor or outdoor trade signs or the like need to have high strength depending on their uses. Hence, the recording media include plastic films or base members coated with plastic films and ink containing a colorant, such as a pigment, having weather resistance is applied to the recording media.
In order to subject plastic films which serve as recording media and which have recording surfaces coated with plastic such as polyvinyl chloride to ink jet recording, a solvent-based ink or an ink, such as a UV curable ink or a two-part curable ink, containing a curable monomer has been conventionally used. The solvent-based ink may stink of solvent or may contain a harmful component such as a volatile solvent component. For the UV curable ink and the two-part curable ink, the curable monomer used may contain a harmful component. If a recording medium having a recording surface which is untreated for ink jet recording and which is a plastic film is subjected to ink jet recording using a known aqueous ink, a print obtained has insufficient weather resistance properties such as adhesion, scratch resistance, and water resistance.
For example, the following composition has been proposed (Japanese Unexamined Patent Application Publication No. 2000-44858 (Patent Document 1)): an aqueous pigment ink-jet ink composition, directly applied to hydrophobic recording media, containing a specific graft copolymer. In this technique, ink is prevented from permeating into a recording medium and a binder is fixed on the recording medium. Hence, there is a problem in that the adhesion of the ink to recording medium is less than that of monomer curable inks such as UV curable inks and two-part curable inks.
On the other hand, for example, Japanese Unexamined Patent Application Publication No. 2002-103785 (Patent Document 2) discloses an ink jet recording ink composition in which a lactam or a lactone can be used as a carrier medium substance (for example, Claim 12 in this document). However, in this document, the lactam and the lactone are cited only as examples of a solvent for dissolving a colorant contained in the ink composition and it is not suggested that a recording medium having a recording surface that is a plastic film is subjected to printing.
Therefore, an ink jet recording method using the following ink has been demanded: an aqueous pigment ink for obtaining a plastic record having high durability and weather resistance properties such as adhesion, scratch resistance, and water resistance.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2000-44858
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2002-103785